An inflator for inflating an inflatable vehicle occupant protection device, such as an air bag, contains a body of ignitable gas generating material. The inflator further includes an igniter. The igniter is actuated so as to ignite the body of gas generating material when the vehicle experiences a collision for which inflation of the air bag is desired. As the body of gas generating material burns, it generates a volume of inflation gas. The inflation gas is directed into the vehicle air bag to inflate the air bag. When the air bag is inflated, it expands into the vehicle occupant compartment and helps to protect the vehicle occupant.
It is desirable that the gas generating material used for providing inflation gas for inflating an inflatable vehicle occupant protection device meet a number of technical requirements such as:
1. The burn rate of the gas generating material must be fast enough to inflate the inflatable vehicle occupant protection device to protect the vehicle occupant.
2. The gas generating material must be chemically and mechanically stable over a wide range of temperatures to be suitable for use in a vehicle.
3. The gas generated by combustion of the gas generating material should be substantially free of toxic materials.
4. The gas generated should be essentially smoke-free.
Solid gas generating compositions based on a non-azide organic fuel component and ammonium nitrate as an oxidizer potentially offer a way to achieve a smoke-free gas that is substantially free of toxic materials. However, many such compositions containing ammonium nitrate as the oxidizer have relatively low burn rates as well as reduced physical integrity when subjected to thermal cycling.
The unfavorable characteristics of ammonium nitrate based compositions can be reduced by selecting organic fuels which contain oxygen atoms. Organic fuels which contain oxygen atoms reduce the amount of the ammonium nitrate that is needed for substantially stoichiometric or complete combustion of the fuel. For example, a fuel like dicyandiamide, which contains no oxygen atoms, may require 85% ammonium nitrate for complete combustion. Nitroguanidine, which contains oxygen atoms, may require only 60% ammonium nitrate for complete combustion. Many fuels containing oxygen atoms, however, are high energy and may be too energetic, or too chemically unstable, for use in a vehicle.
U.S. Pat. No. 5,498,303 discloses the use of a dinitramide salt in a rocket motor propellant. The salt is used as an oxidizer in the propellant to replace ammonium nitrate. The patent mentions ammonium nitrate's poor performance capability, its inability to combust aluminum fuel efficiently, and its low burn rate. Ammonium dinitramide is listed as a preferred oxidizer. However, other dinitramide salts such as tetrazolium dinitramide are also disclosed as substitutes for ammonium nitrate. There is no suggestion in the patent of using a dinitramide salt as a fuel component in a composition having ammonium nitrate as the oxidizer. Moreover, ammonium dinitramide, the preferred dinitramide salt in the patent, in addition to being an oxidizer, is not thermally stable enough for use in a vehicle.